﻿    <p>
      The <em>IfcProductExtension</em> further specialises the concepts of a (physical) product, i.e. a component likely
      to have a shape and a placement within the project context. The product information is provided for individual product
      occurrences as subtypes of <em>IfcProduct</em>, and for common specific product types as subtypes of
      <em>IfcTypeProduct</em>. Both definitions are rooted in supertypes provided within the <em>IfcKernel</em>. Basis
      concepts, introduced within the <em>IfcProductExtension</em>,
      are:
    </p>
    <ul>
      <li>the spatial project structure,</li>
      <li>the element,</li>
      <li>the grid,</li>
      <li>the port, and </li>
      <li>the annotation.</li>
    </ul>
    <p>
      The spatial project structure defines
    </p>
    <ul>
      <li>the site, </li>
      <li>the building, </li>
      <li>the building storey, and </li>
      <li>the space </li>
    </ul>
    <p>
      and its decomposition structure. In addition the concepts of system and zone are introduced within the
      <em>IfcProductExtension</em>. Relationships between the spatial structure and the elements are defined, such as
      spatial containment and space boundaries.
    </p>
    <p>
      An element is assigned to the spatial project structure and may refer by its placement to a grid. Basic types of
      elements, which are introduced are
    </p>
    <ul>
      <li>building element </li>
      <li>opening element </li>
      <li>furnishing element </li>
      <li>distribution element (including heating, ventilation, air conditioning, electrical and equipment elements) </li>
      <li>transportation element </li>
    </ul>
    <p>
      The other concepts introduced are 
    </p>
    <ul>
      <li>a grid, providing a contraint placement for elements, </li>
      <li>an annotation to capture any additional annotations to a building model or plan (such as explanatory text,
      dimensioning, etc.), and </li>
      <li>a port, providing connectivity between elements. </li>
    </ul>